Plastic materials have been used successfully in the past to make formable splints and casts. Some of the plastics that have been used are polyisoprene (U.S. Pat. No. 3,490,444) and polychloroprene (U.S. Pat. No. 3,592,190). Copolymers of trioxane (U.S. Pat. No. 3,604,413) and several other thermoplastics have also been recommended. Recently, poly (epsilon-caprolactone) a crystalline polyester melting at 60.degree. C., and its blends with poly-(vinyl alkyl ether) have been discovered to be excellent splint and cast materials (U.S. Pat. No. 3,692,023). Such a cost has been described in the patent application of Wartman Ser. No. 510,736 filed Oct. 20, 1975. All these polymers have low softening temperatures. In addition, they harden slowly when cooled from the melt to below their softening temperature. They can be heated to a temperature higher than their softening point, allowed to cool in room air temperature, and then molded to the patient without causing discomfort.
Examination of prior art materials based on these polymers in their molten form indicates that they possess another property desirable for easy forming to a smooth surface with good conformity and a lack of wrinkles, indentations or other defects imparted by the hand molding. The molten products do not flow excessively when unsupported by a back-up film, and internal gauze or some such structure. Distortion of the physical dimensions of a molten polymer can take place through viscous flow, elastic flow, or a combination of the two. Some of the prior art products, such as those based on polyisoprene or poly-chloroprene, distort in part by elastic flow. If a strip of molten polymer is manually extended and then released, it has some tendency to return to its original dimensions. However, viscous flow also takes place and permanent distortion beyond the original dimensions occurs. Consequently, when forming these materials, a permanent decrease in thickness can take place. If the therapist inadvertantly stretches the material too much in forming it, the material becomes permanently elongated and unusable for the intended application. Also, reforming a splint, brace, or cast because of a loss of edema in the fitted body member is not possible because, while it is possible to enlarge the structure, reducing its dimensions is not feasible.
In order to provide as stable a structure as possible, so that excessive stretching does not occur in the molten state, the prior art materials generally contain sub-micron sized fillers such as fumed silica, asbestos, clay, or mica. These fillers exert a thixotropic effect and the viscosity, especially at low shear rates, is greatly increased.
This technique is also operable with poly (epsilon-caprolactone). However, considerable quantities of filler are required. About 10% of fumed silica is needed to achieve the required viscosity, while even larger quantities of clay or mica must be employed. Compounding these fillers into the plastic requires sophisticated, costly equipment. The density of the resulting plastic is higher and this is undesirable, because the splint or cast is heavier. Also, the presence of the filler causes the melt to be opaque, so that there is no visual indication that the material has reached the proper temperature for application.
The fillers which are most effective in achieving the thixotropic melt behavior are those with the smallest average particle size. These specialized products are quite expensive and, generally, they do not serve to reduce the cost of the end product. It would be advantageous to achieve the proper rheological properties in the melt using a cheap, larger particle size filler such as calcium carbonate. Heretofore, this has not been feasible because the amounts necessary to attain the proper level of thixotropy are too great and result in a deterioration of the physical properties of the product.
With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.
It is, therefore, an outstanding object of this invention to provide an orthopedic cast, splint, or brace which is clean and simple to apply.
Another object of this invention is to provide an orthopedic cast material which is self-indicating, i.e., is transparent when ready to apply and opaque when non-formable.
A further object of this invention is to provide an orthopedic cast, which is elastic in the molten state and can be reformed to its pre-application shape by remelting and allowing to relax to its original geometry.
Another object of this invention is to provide a cast which has molding characteristics which are relatively insensitive to the temperature of heating and application.
Another object of this invention is to provide a cast which conforms readily to the irregular shapes of the body member to be fitted.
Another object of this invention is the provision of an orthopedic cast which can be applied in a short time.
A further object of the present invention is the provision of an orthopedic cast which is light, strong, and sanitary in use, which allows circulation of air under the cast, and which permits washing of the limb.
It is another object of the instant invention to provide an orthopedic cast which does not require cumbersome equipment to apply.
A still further object of the invention is the provision of an orthopedic cast which reliably adhers to itself during application.
It is a further object of the invention to provide an orthopedic cast which can be applied to the patient while the cast is still in a plastic state.
It is a still further object of the present invention to provide an orthopedic cast which can be pre-formed and which will maintain the pre-formed shape even when rendered plastic.
With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.